For animals crammed in trucks to be transported in hot weather, severe heat stress - which includes symptoms such as panting, salivation, listlessness and lethargy- is common.

Animal activist Stephanie Dyer said there was a desperate need for laws that protect animals from being transported in severe heat.

While animals falling or going down on transport trucks is a problem year-round, Ms Dyer said that if an animal falls or goes down on a truck on a hot day then it is more at-risk of suffocating.

Agriculture Victoria has guidelines in place for farmers and transport operators, including for hot weather, but they are not legal requirements.

These guidelines include considering reducing the number of animals being transported, considering if the route will include traffic and aiming to load and transport livestock in the cooler hours of the day.

But Ms Dyer said this was "pitiful".

"The regulator should introduce laws that make it an offence to transport animals over a certain temperature, particularly when they face a long journey," she said.

Often these animals are being transported to sale yards or abattoirs where they are then placed in pens. Ms Dyer said that in many cases across the state the animals were denied appropriate shelter.

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In its sheep shelter guidelines, Agriculture Victoria states that sheep should be provided with shelter in times of above or below average temperatures to "minimise the impact of climatic extremes and prevent suffering or possibly death."

It also states that it is important that "shelter is available to all animals at the same time to prevent sheep crowding and smothering . It is preferable that shelter includes sufficient room for all animals to be able to lie down, as this helps them cool themselves."

The Industry Animal Welfare Standards define extreme weather as "temperature and climatic conditions that individually or in combination are likely to predispose livestock to heat or cold stress. 'Extremes' of weather can include heavy rain, hail, snow, chilling wind and high heat, all of which can lead to conditions of heat or cold stress in livestock."

With climate change meaning that Victoria's climate will continue to warm, animal advocates believe the time to protect animals from heat stress is now.

Victoria's climate science report of 2019 outlines that "Victoria's climate will continue to warm, with maximum and minimum temperatures increasing over this century".

With an upcoming review into Victoria's animal protection laws and the government to write a new Animal Welfare Act, Western Victorian MP Andy Meddick said that he would be a strong advocate for protecting animals being transported through the law.

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"When it comes to farm animals, their protection under Victoria's animal cruelty laws is near non-existent, and during transport is no exception," the Animal Justice Party MP said.

He said seeing animals being transported in heat and for long distances was "extremely concerning" and that it was common for animals to experience severe heat stress, with some often dying.

"As long as these animals are seen as commodities, or a means to simply make a profit, their protection will always be put last.

"While there are guidelines about how to transport animals during extreme heat - they are not mandatory. That's why I am calling for codes of practice for animals in farming industries to be made mandatory, just like they already are for dogs and cats."

Animals Australia Chief Executive, Glenys Oogjes, urged those involved with livestock to take the weather into consideration.

"We would urge all farmers, agents and truck drivers not to yard and transport animals as the mercury climbs - transport is stressful at the best of times, but the crowding and time off water on these stinking hot days makes it unbearable, even fatal.

"Our laws often fail livestock, but those responsible for their welfare can ensure they do not, through making better choices."

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Victorian Farmer's Federation's Livestock President, Steven Harrison, said farmers and transport operators were diligent about adhering to the guidelines.

"In Victoria they're not travelling great distances and producers and livestock carriers do endeavor to travel in the cool of the day - the welfare of the stock is paramount."

He said he would not be supportive of blanket regulations that ban all sheep transport on hot days, as livestock travel the "length and breadth" of Australia and temperatures varied in different places each day.